Leica M 240 with 35mm F1.4 FLE - some observations

warning: this is a long and head-ache inducingly complex article but it is still not fully comprehensive - there are simply too many variables to test for and give examples of, so I have concentrated on key examples so as to draw what I hope is a general but field-relevant set of conclusions.

I have called this piece 'some observations' because truly bottoming out the performance and the behaviour of some lenses is a Very Big Job - one that requires shooting at every aperture, distance and point of focus and comparing it to an actual or remembered database of peer group lenses. And it's a job that often begins anew when the lens is mounted on a new camera.

The 35 Lux FLE is just such a lens. In a word, it is tricky. Marvellous, wonderful, possessed of impressive technical and artistic qualities, but tricky. And in this it is the diametric opposite of one of the lenses with which I intend to make some comparative observations, the Zeiss 35mm F2 on the Sony RX-1, which is about the least tricky 35mm lens I have used.

A brief historical note: the FLE is a redesign of the previous 35 Lux and has a floating element, aimed at reducing spherical aberrations, in order to reduce the focus shift that plagued the earlier lens.

Lenses have three important dimensions of performance for me: sharpness, beauty of rendering and predictability/consistency. And it must be said that some of the most beautiful renderings go hand in hand with unpredictable and inconsistent behaviours. The 35 Lux FLE is a good example of such.

I'm going to start by showing two files, which can as usual be downloaded at full size by clicking on the images below. They were shot within minutes of each other, on the same tripod, with each camera fitted with its own plate so that as little was disturbed as possible during the switchover. I also made best efforts to position the lenses similarly over the axis of the tripod.

The first is from the M240 with 35 Lux FLE at F4. Focus was on some cobwebby detail in the centre, via live view in the EVF.

Merely looking in detail at these two files (try using the Compare view in Lightroom for example, with the images synched and locked at 100% view and then panning around) will show the trickiness to which I refer. The Sony/Zeiss file is sharp all over, to the edges and corners. The Leica file is about equally sharp at the POF but from there towards the peripheries it wanders in and out of sharpness. No wonder this lens has a 'roller coaster' MTF. For example, the red column of plastic labels mid left is notably soft, the edges are possibly a touch better and the corners are pretty much as good as the Sony Zeiss.

Note that this was focussed with the EVF as described, and was taken reasonably early in my career with the M240, before I realised that the RF is often a better way of focussing - I will come back to that point. I don't have a RF focussed shot of this scene, and I think that it is most likely possible to focus the lens so as to give a better overall balance of focus across the image but what the above examples do show is that the EVF isn't a universal panacea to focus issues and that the lens has an unusual field shape.

That field shape. Hmmm. If only it was in some way consistent from aperture to aperture and at varying subject distances. But it is in fact a slippery bugger, snaking around as you stop down and as you focus at different places within the depth of the scene.

Here is an example at F1.4:

L1000853This was focussed on the near, centre daffodils using the EVF. Observe how the field of focus is croissant-shaped, with DOF extending further away from the camera at the sides.

Shot at F5.6, from a tripod with a levelling base type head (Arca Cube) it was focussed on the left-hand urn with the RF and then recomposed. Observe that the field of focus here is the inverse of the example above: it is now a 'runway', with the ground sharp almost to the extreme gravel corners, the urns sharp, and a cone of focus pointing towards (but not quite reaching) the tower. The trees at the edges are out of focus as is the mid distant grass at the edges.

If you shoot a hundred shots, some with the EVF at shooting aperture and some with the RF, at a variety of distances and a variety of points of focus within the field depth, you will find (or at least I think I have found!) roughly, that:

at F1.4 the field is most often croissant shaped with the arms pointing away, but only if you focus close: the effect diminishes as you focus further away, with the field of focus becoming flatter.

at F2 the field is flatter

at F2.8 and smaller, the forward pointing 'cone' starts to develop but for shots where the POF is at or close to infinity, there is a sub-shape at fF4 and 5.6 whereby the centre area in the immediate foreground is soft and the sides sharper.

Most importantly: if you focus wide open with the EVF before stopping down to at least F5.6 or, more simply, use the RF, then it is usually the case that everything in the same plane as your POF will actually BE in at least reasonable focus, at pretty much any aperture or distance.

Let's look at two aperture series. The first was shot with initial focus wide open confirmed in both EVF and RF on the word 'Pride' on the red umbrella. The aperture was then stopped down for successive shots with no re-focussing between stops. The second was focussed using the EVF and then re-focussed at each full F stop, also with the EVF. I fully expected, given that this lens has slight focus shift, to find that the second series would be better. I was wrong.

Click on the image below to go to a gallery with the entire series. Full sized images can be downloaded for comparison. The images have captions to indicate aperture and shooting method.

The first (no-refocus series) is 'best'. It achieves sharp edges earlier and indeed comparing the two series aperture by aperture, it seems to me that the 'refocussed' series is tending to focus a little closer, bringing the 'cone' referred to above nearer too, and therefore leaving the edges 'outside the cone' such that they are not critically sharp until F8, which is one stop later than the series that was not refocussed between stops.

Diffraction is not an issue until F11 and not a serious issue until F16. Shooting at F8 is therefore indicated for maximum safety if you are seeking planar sharpness without losing out to diffraction

For the curious, this article on the Sony RX-1 lens has a similar aperture series and that lens is sharp to the edges from F2 and notably sharper here than the Leica lens. But as a system, the Leica is resolving a little more on centre across the aperture range: for example, the word Pride on the red umbrella is legible in all the Leica files but merely implied in some of the Sony ones. But the Sony lens is not tricky: you focus it, the subject is sharp. That's it.

The first observation above requires some thought. The poorer performance of the lens when 'stop-down focussed with EVF' is something I have observed time and again in many, many images and there are three hypotheses that spring to mind - and it is possible that they are all factors.

That the EVF is ambiguous at stopped down apertures because it has more DOF within which to report accurate focus and because the resolution of the EVF is not high enough to judge the best point of 'snap'. The shots in the 'refocus' series at f2.8 and F4 might support that, being notably weaker at the edges BUT they are still very sharp on centre so I suspect that the explanation is more due to...

The possibility that the (new?) rangefinder is extremely clever: as we have seen in the field shape examples above, there is a switchover of field shape somewhere around the F2 to f2.8 mark. There is also slight focus shift in the lens (which I will show below). Combinations of focus shift and changes in field shape make lenses notoriously hard to focus such that a planar subject is adequately sharp from edge to edge. If they are focused stopped down on centre, the POF may get placed anywhere within the DOF and that can lead to the edges falling within or outside the field of focus, depending on exactly where the POF ends up. But even a really clever rangefinder has only one choice: at the widest aperture of the lens, there is still some DOF and the RF has to choose whether to place focus towards the front, centre or back of that DOF. If the lens has focus shift, it will be wise to bias towards the front but possibly not too much so: if the field shape changes in a complex manner with changes in aperture, then knowing the parameters of that must inform the decision too.

The chance that the new sensor has a thinner image receiving layer and can therefore tolerate less accurate placement within the DOF of the image as projected onto it.

Whatever combination of these, or other, factors is at work (and actually there is a possible inconsistency: the EVF/refocus shots seem to focus a touch closer, which is what I expect to see the RF doing from its performance at closer ranges - maybe the RF is even smarter than I think!) this setup really works: I find that RF focus gives the best results with this lens, closely followed by EVF focus 'wide open before stopdown', with EVF focus at shooting aperture a less satisfactory third place.

{NOTE: I refer here to the RF being clever but that is shorthand. The rangefinder has to do the same thing in response to inputs from every lens it encounters so the cleverness lies in the exact design of the cam inside the lens mount that transmits information to the RF roller. It is that and the accuracy and repeatability with which the RF responds to it, which determines exact placement of the POF in the DOF for each specific lens.}

On to Focus Shift

The following series of crops, shot with focus made by the rangefinder, shows that the focus shifts slightly backwards as the lens is stopped down but that the POF always stays within the DOF. Starting at F1.4 and then stopping down through full stops to F8. I will link to the series here for you to download, if interested, and look at in an appropriate viewer by tabbing through them at 100% view. If you do you will see that the point of focussed is biased towards the front of the DOF wide open and then moves progressively backwards but always remaining within the DOF. This shows an ideal calibration of the rangefinder to the lens. {Note: I inadvertently shot this series in Auto ISO so the files increase in ISO as I stop down, giving an exaggerated impression of increased acuity. Please see this series as an example of the positioning of focus, not the absolute degree of acuity.}

Here is a series from F1.4 thru F8. It shows that the colour shading is not defeated but quite well controlled, probably a little more so than in the RX-1. It is shot at a cloudy mid-morning sky through a Phase One Lens Cast Calibration sheet, a thick piece of optically neutral perspex that completely diffuses the light.

L1000821L1000822L1000823L1000824L1000826L1000827

Chromatic Aberration

The lens has shows notable fringing at F1.4, but it cleans up well well from F2 onwards and is quite easily dealt with in post. I show first a crop from the 35 Lux FLE and then a crop from the same scene shot with a Sigma 35mm F1.4 HSM ART lens on a Nikon D800E, also at F1.4

L1000849-2_DSC9358Distortion

The lens has moderate distortion only, and unless you are shooting flat horizons or architecture, you will not need to correct it. LR 4.4 has the correct profile and I show an uncorrected and then a corrected scene to show the effect.

L1000854L1000854-2

Bokeh

Lens designers have to make an awful lot of decisions. If they want a fast wide lens, then ceteris paribus they will risk more distortion, field curvature, spherical aberrations (possibly leading to focus shift) and chromatic aberrations. Physics can only be pushed so far. On top of this, there is the desire to achieve flare resistance, light weight, focussing accuracy etc. etc... and then there's the problem of bokeh, which might end up looking nasty. Bokeh is damned complicated: are the OOF highlights round, elliptical or polygonal, and if polygonal, how many sides are visible? Are they smooth or 'doughnut' shaped? How do strong lines or grids appear when when they are OOF? How quickly and smoothly does focus fall away? And who prefers which mix of these characteristics? In other words, it is part science and part personal, artistic preference.

The 35 Lux FLE has 9 blades and bokeh which is quite nice but not perfect, to my eye. It has nice falloff, but it renders OOF highlights with a 'doughnut' tendency and it renders OOF lines rather busily. In fact, its bokeh overall is a bit too busy to fully satisfy me.

Here is the same shot taken with the 35 Lux and with the Sony RX-1 at F2, their widest common aperture, followed by crops.

L1000788

_DSC1279L1000788_DSC1279To my eye, the RX-1 looks nicer.

Now for OOF strong line rendering: again, Leica then Sony but no crops this time - the effect is visible at almost any size.

L1000792

_DSC1280Again, IMHO the Sony wins: it is less 'hectic' in this respect, though it has a less rapid falloff, evident more in some shots than others, which gives the impression of more DOF. In fact the field of view of the Sony lens is wider than 35mm - I suspect that it is closer to 31 or 32mm and this will indeed give it more DOF (and might contribute to its apparently better average sharpness across the frame at wider apertures) than the 35 Lux on the M 240.

I no longer have the Sigma 35mm F1.4 lens for my Nikon D800E so I cannot provide comparative shots but its rendering of bokeh is really quite similar to the 35 Lux: a little nervy, but with very nice falloff. Both lenses can go to F1.4 rather than the F2 of the Sony, so they can both be made to look more obviously 'arty' but the actual quality of the bokeh is IMHO best on the Sony.

Conclusion

The 35 Lux is a very, very important lens for the M system: it is the classic 'street shooting and reportage' focal length and Leica's reputation rests quite heavily on its ability to make very fast lenses that are small, light, sharp and accurate. Hence, I believe, the priority given to redesigning the 35 Lux when its predecessor's weakness on digital sensors first became evident. So, how did they do?

Given the constraints, very well indeed. The lens is very good. But it is not as good as I would like. As noted serially above, it has a 'tricky' field of focus such that to be sure of capturing planar subjects on the M 240, an aperture of F8 is IMHO needed. It has somewhat busy, nervy bokeh and it has quite a lot of colour fringing and colour shading wide open. But no one can work miracles and it is clearly a good compromise between differing performance requirements - and one which is well suited to the Leica gestalt of small, light, fast, very sharp (at least on centre) at every aperture and pleasingly artistic.

I also think that the artistic impact of a lens does not just depend on its bokeh and its colour characteristics: I think that a curved field of focus can be creatively very beautiful - it can literally focus attention on the subject if well used, and have that subject surrounded by an attractive glow of slight OOF. It can also create dream-like fields of focus where nothing is quite as you might rationally expect.

For that reason, I think that it is a great lens, on the M240, for beginners and experts. Beginners will be unlikely to notice the problems and will merely get a lot of lovely Leica Look for their money. Experts will quickly recognise and learn how to work around and then positively use its complexities. But intermediate photographers, those with enough experience to know when something is 'off' but not enough to work out exactly what or why, will be better served by the lens on the RX-1, with its un-fussy ability to place focus exactly where you expect it to, time and again.

Finally: I think the 35 Lux FLE is both a better and a worse lens on the M 240 than on previous digital Ms. Better because for me, the new camera, whether through its rangefinder mechanics or the thickness of its sensor - or whatever other factor - makes this lens significantly easier to focus predictably. Worse because the extra pixels mean that at a pixel level, the odd field of focus effects (such as those in the example at the very top of this page) are more evident. Of course if you don't print any larger with the M 240 than you did with the M9 or M8, you won't notice a difference in a well-focussed file. But if you scale your print size with your pixel count, you will.

In the end, we all make system choices, not just lens choices. For my purposes I would prefer to shoot the Sony RX-1 or the Nikon D800E with a good copy of the Sigma 35 F1.4 HSM, with which it has much in common. But for those who love the M form factor and the rangefinder style of shooting, this lens is a cracker.

I would appreciate it if others using the M240 and 35 Lux FLE shared their experience in the comments section below, and if people interpret the examples I give above in a different manner to that in which I have seen them, please add your insights - this is a complicated lens and many heads are better than one!

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ADDED 13th April 2013

I have run a very extensive re-shoot test of the big white wall chart that has created so much comment, concern and correspondence. This time I filled the frame with the chart rather than including it as part of a slightly wider scene. It is very very slightly bowed in places but tight to the wall in enough comparable places and I wouldn't regard this as a very significant factor. I took a very great deal of care to get as accurately lined up to the subject as possible, using the Horizon feature and very many repositionings of the tripod and head until I got it square - not an easy task since the Live View gives a slightly different FOV to the recorded file.

I then shot many series of F1.4 thru 16 and it will take quite a while to analyse the results so for now I have looked at the F4 results, since those are the ones that have sparked the controversy.

I shot these series:

Focussed through EVF wide open and not refocussed as I stopped down

Focussed through RF and that focus kept for all shots

Focussed through EVF and refocussed between aperture changes

Ditto for a second run

Focussed through EVF and refocussed between aperture changes (focus 'coming from NEAR to 'first shimmer')

Focussed through EVF and refocussed between aperture changes (focus 'coming from FAR to 'first shimmer')

A series only at F4 where I tweaked focus minutely across many frames from near to far

Series 3) above replicates the focus method used in the original review. I quote myself from that piece:

"Note that this was focussed with the EVF as described [focus stopped down to F4, shot at F4] and was taken reasonably early in my career with the M240, before I realised that the RF is often a better way of focussing - I will come back to that point. I don't have a RF focussed shot of this scene, and I think that it is most likely possible to focus the lens so as to give a better overall balance of focus across the image but what the above examples do show is that the EVF isn't a universal panacea to focus issues and that the lens has an unusual field shape. "

What I found today was that this is pretty much exactly true. But there were other useful lessons: (all regarding the F4 only shots so far pending review of all 60 frames)

Focussing wide open with the RF or EVF gives much better results across the frame. Pretty much all of the frame is between very acceptable and excellent, especially viewed at print resolution or 50% view

Refocussing at F4 with the EVF gives, if anything, sharper results on centre but a repeat of the 'wandering in and out of focus across the rest of the frame' seen in my original shot

Reaching stopped-down EVF focus from 'far to first shimmer' gives equally good results to the RF focussed shot across the frame

Reaching stopped-down EVF focus from 'near to first shimmer' gives equally good results to the RF focussed shot on centre but very poor results across large parts of the frame

From this I conclude provisionally that my fist instincts were right: there is an uneven field of focus, probably wave shaped, and that when stopped down to F4 it is of a shape such that the EVF provides too much ambiguity to focus stopped down, because the POF needs to be focussed towards the back of the DOF in order to get as much of the planar target as possible within the field of focus.

This will be somewhat counter-intuitive to some users who, assuming that because the lens has a slight tendency to shift focus further away as one stops down, will feel that the safest way to focus is 'stopped down EVF'. In fact, because the actual point of focus remains (laudably) within the DOF as you stop down, despite this focus shift, one needs to be more concerned about focussing according to the 'shape' of the field of focus and this requires one to bias focus towards the rear of the field.

When you focus with the very accurate RF, or with the EVF wide open, this process then happens naturally: you stop down without changing focus and the lens's inherent focus shift moves so as to bias the POF rearwards within the field, thus compensating really nicely for the shape of the field.

But when you focus with the EVF stopped down, it is a crapshoot biased toward failure: coming at focus from FAR to 'first shimmer' gives a very good result but from NEAR to first shimmer, gives a good centre and a very poor average across the frame.

So: using the RF, the EVF wide open or the EVF stopped down but with a far bias are the best ways to get good results across the frame.

Phew.

Images, just two for now. Both at F4. The first is focussed EVF wide open and the second is one of two series I shot with the EVF stopped down but is typical of both those series.

This is 'angels on pinheads' territory for many users and I do think that individual pairings of particular cameras and lenses will vary, but I think many users will get similar results and I do think that knowing this stuff, if it does hold true in a more general sense than my particular use-case, will help those who seek the best sharpness across the frame to achieve it.

One final note: the frame that was very sharpest on centre (by a tiny margin) did not have the best average performance across the frame. There is, as far as I can see, no possible focus setting that would achieve that, which is exactly what I would expect and is just not going to matter in practice!

Comments

"I could hardly believe how badly the Leica lens performed particularly on planar subjects"

The above quote was my reaction to Tim's findings. Having now used the Leica M 240 with 35mm F1.4 FLE for around 9 months I felt I needed to update my reaction based on my own findings.

To summarise I find that for critical needs the lens needs to be focussed very carefully with the EVF at the taking aperture using the magnification facility. I also find that by f8 curvature of field is no longer an issue.

Thanks

Keith

34.jack(non-registered)

This is an interesting article. I own and use both the new 35fle and the 35cron, and there are characteristics about both that I like. The fle, when one has the time to adjust for its characteristics, can produce lovely and striking results, as you correctly point out. The 35 cron is not capable of such heights (but is nonetheless exceptional) but is far easier to shoot, especially for street shooting. I find that the color rendering of the fle is superior. When using the fle for a composed, carefully imagined landscape I have learned to shoot it the way you describe in your excellent review. In general, however, for most of my work I prefer the new 50 Cron APO which delivers the best and most predictable all around results.

33.CT(non-registered)

I have this lens and it definitely displays field curvature. It's similar to the Nikkor AIS manual focus 35mm 1.4 which also has the same type of characteristic. I have always called the Nikkor my 'cowboy hat lens' since the shape is kind of like a hat. I don't own a digital Leica but use the FLE lens on the M4 and M6 film bodies. The Nikkor I use on both the F3 and the D800E. Once you understand this curvature, it's really all okay and the lens will provide excellent results. I like them both quite a lot. And I don't think that this phenomenon is that unusual for wide angle lens. All lens designs are a trade-off.

32.Dez(non-registered)

It is normal behavior for the Leica 35mm Summilux to show strong field curvature, one only needs to look at the MTF charts to see that. The lens was originally designed for film, which is not as sensitive to field curvature as a digital sensor for two reasons. 1) Film is not flat like a sensor 2) Film has depth in the emultion. When people started complaining about focus shift on the M8 and M9 (which was also not as much an issue on film because of the above reasons), Leica did a quick revision to modify their design to use floating elements but they did nothing to cure the field curvature. Zeiss, in order to not have these same issues, designed a lens that was significantly larger than you would expect for a non-retrofocus design. This is in line with Zeiss' philosophy of "design relaxation" where, instead of using expensive exotic glass, or equally expensive Aspherical elements, they spread the duties of image correction across more elements and sometimes larger elements. Leica's philosophy is to use as few glass elements as possible, so they use more exotic glass and ASPH surfaces. If you look at the rear element from the Zeiss 35mm f/2 on the RX1, it's absolutely huge and that's to direct the light hitting the sensor as dead-on as possible. This helps to mitigate things like light falloff, field curvature, color shifts and softness in corners. They also made the decision to have a maximum aperture of f/2, which is a much more relaxed design than f/1.4. If you were to compare the Leica 35mm Summicron ASPH, which is an f/2 lens, to the Sony, you would see a much flatter field of focus. You would still see the same oval and outlined OOF highlights as the Summilux though, as that is a tradeoff for using ASPH elements. This is the reason I use the Zeiss Biogon 2/35 on my M9 for landscape and architectural work. Although it is not quite as sharp at f/2 as the Leica Summicon or Summilux, it has a much flatter field of focus and almost zero distortion. That being said, the 35mm Summilux is my favourite lens for everything else and I wish I still had access to one.

31.Tim Ashley Photography

I had a private post to this thread from a Mr X which I thought I would answer publicly (if anonymously on his side) because it is of general interest and because the sender's email address is broken!

Question:&quot;I don't have a 240 yet, but just an observation of using this lens on my M9. The third copy I tried I bought, the other two left me unimpressed. I don't know why this would be true.&quot;

Answer:Dear Mr X,

I am currently on my fifth copy of the Sigma 35mm F.14 Art lens for Nikon and finally I think I have a good one.

There are many reasons why multiple poor copies might appear: a poor construction run; a design which is more ambitious than production can easily achieve; a design prone to transit induced problems; the possibility that body/lens interactions are very specific (for example the way in which a rangefinder is calibrated.) And so on…

It is part of my job and my interest to 'sniff out' which characteristics of a lens are unique to that particular copy, which might be due to a lens/body interaction and which are just characteristics of the design in general. After a while you develop a sixth sense for it. And I am pretty confident that this is a representative sample of a correctly assembled and quality controlled product. Most fast, wide lenses have some complex behaviours and the 35FLE is simply no exception!